Signalling System microcontrollers connect to items of signalling equipment using "CAN Bus", a simple network connection with simple wiring and easy to follow rules. Instead of having large bundles of wires being routed around the site, using the CAN bus network most of the site wiring fits into just two cales - a CAT6 network cable and a power distribution cable.
To date we have CAN bus twin lamp LED signal heads ready for production.
Other essential elements of signalling equipment (including points actuators and axle detectors) are yet to materialise, but these will be built to include the necessary CAN bus interface.
The one exception is in the area of the signal box and level crossing where input/output expansion modules are provided to allow direct connection of switches, sounders and similar.
CAN Resources
CAN Bus tutorial from controllerstech.com
STM32L4 HAL and Low Layer User Manual.